1. Field of the Invention
The present invention relates to a common mode choke coil for eliminating common mode noise.
2. Description of Related Art
FIG. 6 shows an equivalent circuit of a conventional common mode choke coil, and according to the figure, coils L11 and L12 are arranged facing to each other such that magnetic fluxes in mutually opposite directions will be generated around the coils L11 and L12.
FIG. 4 shows a common mode choke coil 30 which has a structure which can realize the equivalent circuit shown in FIG. 6. A couple of cores 31 and 32 shaped like E are butt-jointed. The center legs 31a and 32a of the cores 31 and 32 are wound with coils L11 and L12 respectively such that magnetic fluxes in mutually opposite directions will be generated around the coils L11 and L12.
The coils L11 and L12 are disposed on the same axis, and thereby, the common mode choke coil 30 obtains an advantage that the leakage of magnetic flux is small.
FIG. 5 shows a common mode choke coil 40 which has another structure which can realize the equivalent circuit shown in FIG. 6. A couple of cores 41 and 42 shaped like U are butt-jointed. Mutually butted legs 41a and 42a of the cores 41 and 42 are wound with a coil L11, and the other mutually butted legs 41b and 42b of the cores 41 and 42 are wound with a coil L12. The coils L11 and L12 are wound such that magnetic fluxes in mutually opposite directions will be generated around the coils L11 and L12.
The legs 41a, 42a, 41b and 42b of the cores 41 and 42 are extended by the butt joint, and the coils L11 and L12 are disposed on the extended legs. Accordingly, the coils L11 and L12 are long enough such that the common mode choke coil 40 obtains an excellent frequency characteristic. Higher the frequency characteristic is, more excellent the performance of the common mode choke coil is.
In FIGS. 4 and 5, arrows indicate directions of magnetic fluxes generated around the coils.
The above-described conventional common mode choke coils have disadvantages as follows.
The common mode choke coil 30 shown in FIG. 4 uses the E-shaped cores 31 and 32, and the coils L11 and L12 wound therearound are not sufficiently long. Accordingly, the common mode choke coil 30 has a poor frequency characteristic.
Regarding the common mode choke coil 40 shown in FIG. 5, magnetic fluxes leak from the coils L11 and L12 in the same direction, which brings a synergetic effect. Consequently, the leakage of magnetic flux becomes large.